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Hi Furseo I would say that it has the potential to affect your SEO as you are not able to close the pop up without selecting a city. I do not live in any of the cities listed so I can't navigate your website. Google will penalise sites which it deems are obscured behind an intrusive pop up. You can read more about interstitial ads and pop ups here: https://webmasters.googleblog.com/2016/08/helping-users-easily-access-content-on.html If you want to ask then have a pop up that can be closed by the user. Having a sniffer on the site is not always a good idea as servers can be hosted in different locations to the user. Kind Regards Nigel